Exhaust system for furnace retort

ABSTRACT

A SYSTEM FOR SCRUBBING WASTE GAS FROM A METAL TREATING RETORT AND REGULATING THE PRESSURE IN THE RETORT INCLUDES APPARATUS FOR WITHDRAWING THE GAS FROM THE RETORT AND COOLING THE GAS. THE COOLED GAS IS TRANSFERRED TO A LIQUID SEALING VESSEL CONTAINING A GAS DIFFUSING STRUCTURE, GAS EXHAUST TUBE, LIQUID DISCHARGE TUBE LEADING TO A SECONDARY SEAL OR DRAIN, AND A COMMUNICATING LIQUID LEVELING VESSEL. THE LEVELING VESSEL IS EQUIPPED WITH AN ADJUSTABLE DRAIN AND AN INLET FOR INTRODUCING FRESH LIQUID.   D R A W I N G

March 20, v H K YQUNG ETAL EXHAUST SYSTEM FOR FURNACE RETORT Filed Oct. 30, 1967 2 Sheets-Sheet 1 FIGI fin INVENTORS HAROLD K. YOUNG HERBERT WALD Man-ch20, 1973 YQUNG ETAL EXHAUST SYSTEM FOR FURNACE RE'IORT Filed Oct. 50, 1967 2 SheetS -Sheet 2 FIGZ I 35 1 1 f as I n INVENTORS HAROLD K. YOUNG HERBERT WALD United States Patent 3,721,429 EXHAUST SYSTEM FOR FURNACE RETORT Harold K. Young and Herbert Wald, Baltimore, Md., assiguors to Bethlehem Steel Corporation Filed Oct. 30, 1967, Ser. No. 678,829 Int. Cl. 301d 47/02 US. Cl. 261-123 4 Claims ABSTRACT OF THE DISCLOSURE A system for scrubbing waste gas from a metal treating retort and regulating the pressure in the retort includes apparatus for withdrawing the gas from the retort and cooling the gas. The cooled gas is transferred to a liquid sealing vessel containing a gas diffusing structure, gas exhaust tube, liquid discharge tube leading to a secondary seal or drain, and a communicating liquid leveling vessel. The leveling vessel is equipped with an adjustable drain and an inlet for introducing fresh liquid.

BACKGROUND OF THE INVENTION This inveniton relates to the gas exhaust system of a treatment retort and more particularly to a liquid sealpot used in connection with such system.

Various means have been employed to control and maintain pressure of the flow of exhaust gases from treatment retorts. The exhaust gases themselves may be deleterious to the articles treated in the retort, and thus must be withdrawn continually. Certain waste gases contain matter which is objectionable when discharged into the atmosphere and these gases require scrubbing before such discharge.

In the process as chromizing, wherein steel strip is chromized in an annealing retort, a positive pressure should be maintained at all times within the retort. Positive pressure is generally maintained by means of a liquid seal. Because of the high temperature of the effluent gases, and the chemical constituents which these waste gases contain, conventional liquid seals have not proved entirely satisfactory.

It is an object of this invention to provide a retort gas exhaust ssytem which will maintain proper back pressure in the retort.

Another object is to provide an efi'icient liquid seal for the exhaust system.

A further object is to provide a liquid seal which requires very little maintenance.

SUMMARY OF THE INVENTION We have found that the foregoing objects can be attained by use of a liquid sealpot of special design in conjunction with a liquid level tank and a settling vessel.

The invention comprises, broadly, exhausting Waste gas from a metal strip heat treating retort into a jacketed vessel where the gas is cooled somewhat while circulating in the vessel, and is then exhausted from the vessel to a liquid sealpot. The gas enters the sealpot below the liquid level, and is well distributed through the liquid by means of a gas difiuser. The gas is scrubbed in the liquid and leaves the sealpot by way of a tube, or pipe, having its entry end located above the liquid level. The liquid level in the sealpot is maintained by a liquid communication therewith. Liquid is withdrawn slowly and uniformly from the sealpot to remove impurities therefrom, and liquid is introduced into the liquid level tank at a slightly higher flow rate.

The invention provides for a constant pressure in the heat treating retort and simultaneous removal of impurities from the foul waste gas, the soluble impurities 3,721,429 Patented Mar. 20, 1973 being discharged with the scrubbing medium. The gas, which is ultimately exhausted to the atmosphere, is relatively free of objectionable components. The sealing and scrubbing device requires very little maintenance.

BRIEF DESCRIPTION OF THE DRAWING The improvement of this invention will be brought out more clearly in the following specific example.

Referring to FIG. 1 of the drawnig, waste gas is discharged from a heat treatment retort 10, located under furnace cover 9, by way of pipe 11. The waste gas contains hydrogen and volatile chlorides of manganese, iron and chromium. The chlorides are formed in the retort during a chromizing operation, which comprises, in this example, sintering of a ferrochrome powder coated coil of low carbon steel strip for about 30 hours at elevated temperature. The chromizing is performed in an atmosphere of hydrogen which contains a small percentage of chlorine. Hydrogen and chlorine are introduced into the retort continuously during most of the actual sintering treatment at pipes 13 and 14 respectively. Hydrogen and chlorine are applied to the retort to assure an oxygenfree atmosphere therein, and, to obtain full effectiveness of these gases, a positive pressure should be maintained in the retort.

The waste retort gas passing through pipe 111 enters settling bottle 15 through inner chamber 16 and leaves the bottle by way of outer member 17 and pipe 21. Some particles in the waste gas consisting of reaction products of chlorine, are deposited in bottle 15. As the outer chamber 17 is surrounded by a water jacket 18 supplied with circulating water entering at inlet 19 and exiting at 20, the gas, which leaves the furnace at a temperature in the neighborhood of 1400 F., enters pipe 21 at a temperature of about 400 F. The cooled gas is conducted to sealpot 22 by way of pipe 21 which extends below the liquid level of the sealpot. As additional solid matter deposits in pipe 21, backwash connection 23 is provided for periodic flushing of the pipe.

Referring now to FIG. 2, it will be seen that the gas discharged from the bottom of pipe 21, under the level of the sealpot liquid 24, is dispersed in the liquid, which in this example is water, by means of gas diffuser 25. The diffuser has stationary vanes 26 of fii-inch carbon steel which are shown more clearly in FIG. 3. By means of the dilfuser, the gas is mixed sufiiciently with the water inthe sealpot to remove substantially all of the unused chlorine and soluble chlorides from the gas. The scrubbed gas, now containing mostly hydrogen, rises to the top of the sealpot, where it enters pipe 27, and from there is discharged to the atmosphere. The water level in sealpot '22 must be maintained above the exit end of incoming gas pipe 21, and below the entry end of outgoing gas pipe 27.

In order to maintain the liquid level in sealpot 22 at a constant, desired level, a constant liquid level tank 28 is employed adjacent sealpot 22. Liquid level tank 28 is in liquid communication with sealpot 22 at opening 30. The desired liquid level in sealpot 22 is regulated by the liquid level in tank 28. An adjustable pipe 31, operating in casing 32, can be raised or lowered to the predetermined water level. Water is introduced into liquid level tank 28 from pipe 33 regulated by valve 34. Preferably, a constant flow of water is introduced into tank 28, in an amount which compensates for water lost from the tank at pipe 31 and from the sealpot at pipe 35. Pipe 35, which is located below the desired liquid level of sealpot 22, and above communicating opening 30, provides a means of constantly drawing water containing dissolved salt from the sealpot. Pipe 35 empties into secondary seal 36 below the level of the water 47. Water leaving seal 36 at outlet 38 is discharged to liquid waste disposal. The entry end of pipe 35 is located above opening 30 to prevent evacuation of sealpit 22 if the supply of waer from pipe 33 to liquid level tank 28 is interrupted.

In sealpot 22, as shown in FIG. 2, the sealpot wall 40 is constructed of 16-inch outer diameter carbon steel pipe having a thickness of inch. The sealpot is closed at the bottom by a y -inch thick carbon steel plate 41. Openings are provided in plate 41 for the welding thereto of l-inch pipes 35 and 42. Pipe 42, fitted with plug 43, acts as a drain when cleaning the sealpot. A /2-inch plate 44 is bolted by eight bolts 49 to flange plate 47, which is in turn welded to the top of sealpot wall 40. A rubber gasket 39 acts as sealant between flange 47 and plate 44. Openings are provided in plate 44 for gas entry pipe 21 and gas exit pipe 27, both of which are welded to plate 44. Pipes 21 and 27 each have a diameter of 3 inches, and are constructed of Az-inch carbon steel. An additional opening is provided in plate 44 for a lVz-inch pipe 45 for flushing and inspection of the sealpot. Pipe 45 is fitted with plug 46.

Water level tank 28 has a bottom plate 48 of the same material and thickness as plate 41. The walls of tank 28 are constructed of three fiat A-inch thick plates and a portion of wall 40 of sealpot 22. Referring to FIG. 4, plates 51 and 52 are welded to plate 50, and each is welded to bottom plate 48. This entire construction is welded to a portion of wall 40 and bottom plate 41 of sealpot 22.

The secondary seal 36 is used as a safety precaution, in the event the water supply from pipe 33 is interrupted. In such case, without seal 36, pipe 35 would drain empty and break the seal in sealpot 22.

By use of our invention, positive pressure is maintained in the retort during the sintering operation, thus preventing introduction of air through possible small leaks in the retort. The waste gas is scrubbed and chlorides removed therefrom so that substantially only hydrogen is vented from the system as vapor, the water discharge containing chlorides being sent to liquid waste disposal.

By use of our system, the moisture level in the sintering, heat treating retort, does not increase during heating of the furnace up to 1700 F., indicating that no moisture is drawn into the furnace from the sealpot.

There is practically no maintenance on the sealpot other than periodic water flushing.

To avoid the possibility of the already cooled gas from bottle acquiring a greatly increased temperature from radiant heat from the furnace wall, either the sealpot may be located a proper distance from the furnace, or a shield may be placed between the furnace and the sealpot and connecting line 21.

We claim:

1. In a system for scrubbing the efiluent gas from a heat treating retort and regulating the pressure in said retort, the apparatus comprising means for withdrawing gas from said retort and discharging said gas downwardly into a vertically disposed inner tube of a water cooled settling vessel, said tube being open at the bottom and spaced apart from the walls of said vessel, cooling means surrounding said vessel and gas exhaust means near the top of the outer wall of said vessel, a connecting gas entry tube joining said exhaust means with a liquid-containing sealpot and extending downwardly into and exiting below the liquid level of the sealpot, a gas exhaust tube located above the liquid level of said sealpot, a gas difiusing means located below the outlet of the connecting tube, a liquid exhaust tube for constant withdrawal of liquid from the sealpot wherein the inlet of said exhaust tube is located below the liquid level of the sealpot and above the outlet of the gas entry tube and the outlet of said exhaust tube is below the liquid level and the liquid outlet of a secondary liquid seal, and a liquid passageway connecting the liquid in said seal pot with the liquid in a constant liquid level tank, said level tank being fitted with an adjustable level drain and means for supplying a constant flow of liquid to the tank.

2. A system according to claim 1 in which the liquid in the sealpot and level tank is water.

3. A sealpot and level tank comprising a liquid-containing sealpot having a gas entry tube existing below the liquid level of the sealpot, a gas exhaust tube located above the liquid level of the sealpot, gas diffusing means located below the exit end of the gas entry tube, a liquid exhaust tube for constant withdrawal of liquid from the sealpot wherein the inlet of said exhaust tube is located below the liquid level of the sealpot and above the outlet of the gas entry tube and the outlet of said exhaust tube is below the liquid level and the liquid outlet of a secondary liquid seal, and a direct liquid passageway connecting the liquid in said sealpot with the liquid in a constant liquid level tank, said passageway being located below the gas exhaust tube and the entry end of the liquid exhaust tube, said level tank being fitted with an adjustable level drain and means for supplying a constant flow of liquid to the tank.

4. Apparatus according to claim 3 in which the liquid in the sealpot and level tank is water.

References Cited UNITED STATES PATENTS 2,274,006 2/1942 Smith 261-121 R 2,485,835 10/1949 Mabeth 261-121 R 1,411,150 3/1922 Barnstead 55-269 UX 1,912,381 6/1933 Meston 55-269 X 1,927,529 9/1933 Pratt 261-121 2,403,545 7/1946 Nutting 261-72 X 2,423,794 7/1947 Otto 261-121 X 2,721,065 10/1965 Ingram 261-124 3,045,996 7/1962 Rice 266-31 FRANK W. LUTTER, Primary Examiner R. HALPER, Assistant Examiner US. Cl. X.R. 

